The error message had gone this morning and I thought it was all sorted but now it is back again. I can't find what it means in any "help" or any other posts. Hopefully someone can tell us how to fix it!

Thanks for your reply.
When I looked at my website again this morning (just now) there is no error message showing again. It seems weird that it comes and goes.

Could you please elaborate on what you suggested in case the error message comes back? Where do I find the wp-includes folder and how do you upload an individual folder. I am pretty new to Word Press and still finding my way around it. Thanks.

The theory was that something had corrupted some of the WP core files (although, in this case, it would seem like it was a temporary server issue). The sub-folder wp-includes contains many scripts that are used to run both the front end of the site and some of the back end Admin area. If some of those files are damaged, the easiest option is to: